It is well known that the components of most pneumatic tire constructions must be assembled in a way which promotes good tire uniformity in order to provide proper tire performance. For example, a tread which “snakes” as it goes around the tire circumference will cause wobbling as the tire is operated. For example, a carcass ply which is lopsided (longer cords on one side of the tire than the other side) can cause a variety of tire nonuniformity problems including static imbalance and radial force variations. For example, a tire which is not meridionally symmetric (e.g., tread not centered between beads) can cause a variety of tire nonuniformity problems including couple imbalance, lateral force variations, and conicity. Therefore, in order to meet typical tire performance requirements, the tire industry generally expends considerable effort in producing tires with good uniformity. Tire uniformity is generally considered to mean tire dimensions and mass distributions which are uniform and symmetric radially, laterally, circumferentially, and meridionally, thereby producing acceptable results for measurements of tire uniformity including static and dynamic balance, and also including radial force variation, lateral force variation, and tangential force variation as measured on tire uniformity machines which run the tire under load on a road wheel.
Although certain degrees of tire nonuniformity can be corrected in post-assembly manufacturing (e.g., by grinding), and/or in use (e.g., applying balance weights to the rim of a tire/wheel assembly), it is preferable (and generally more efficient) to build-in tire uniformity as much as possible. Typical tire building machines comprise a tire building drum around which the tire components are wrapped in successive layers including, for example, an innerliner, one or more carcass plies, optional sidewall stiffeners and bead area inserts (e.g., apex), sidewalls, and bead wire rings (hereinafter simply referred to as “beads”). After this layering, the carcass ply ends are wrapped around the beads, the tires are blown up into a toroidal shape, and the tread/belt package is applied. Typically the tire building drum is in a fixed location on the plant floor, and the various layers of components are applied manually or automatically using tooling registered to reference points on the fixed drum in order to ensure component placement with the desired degree of precision. The tooling is generally fixed relative to the tire building drum, for example a guide wheel on an arm extending from the same frame (machine base) which supports the tire building drum.
The tire building drum must be supported in a way that allows beads, which are complete circles or rings, to be applied on the tire carcass as it is built in layers that are wrapped on the tire building drum. Also, there must be a way to remove a green tire when the tire building process on the tire building drum is completed. The tire building drum may be permanently supported on only one end, thereby creating a “free end” over which the beads may be applied, and the green tire may be removed. This single-ended support is commonly known as a cantilever mounting. An everyday example of a cantilever mounting is a diving board.
Various problems must be addressed for a cantilever mounted tire building drum, especially considering tire industry requirements for the uniformity of tires built on the drum, and also desires for durability of the manufacturing equipment. For example, large force moments are created on a cantilevered tire building drum support due to factors including the weight of the tire building drum, the weight of the tire components applied to the drum, and lateral forces (i.e., forces in any direction radial to the tire building drum axis of rotation) from the tire component application equipment (e.g., stitching rollers that press the components together). In cases wherein the tire building drum rotates during the tire building process, then these force moments can cause problems (e.g., unusual wear) for bearings positioned in the support to facilitate rotation of the drum. Tire uniformity is affected if the tire building drum is allowed to bend in response to the forces bearing on it which could, for example, cause a tire layer to be laid in a spiral. For a cantilever mounted drum, the bending could be along the length of the drum and/or could be involve pivoting where the tire building drum is held by the permanent support. To stabilize the tire building drum, i.e., to prevent drum bending and/or other undesirable movement, a cantilever mounted tire building drum must be more rigid and must involve much more substantial bearings and other connections to the single end support than comparable tire building drums that are supported on both ends. Obviously, such increased robustness costs more, generally adds to the overall weight, and produces equipment which is more complex and therefore more difficult and expensive to maintain. Finally, the present invention addresses the additional problems of cantilever mounted drum stabilization that arise when the tire building drum is no longer fixed, but instead is a work-piece in a flexible manufacturing system (FMS) wherein the building drum is moved between automated work stations for application of successive component layers in successive work stations. The context of the present invention is an FMS having work-pieces (tire building drums) which are too large to allow the use of a precision pallet conveyor, so the tire building drums are moved (propelled) by other means which are not necessarily able, by themselves, to achieve sufficient accuracy in positioning the tire building drums relative to the work stations. The work stations each have a centerline, or “working axis” of the work station tire assembly devices (tools), and the axis of the tire building drum must be precisely aligned with the working axis in each work station. Such alignment includes assuring that each point along the entire drum length of the tire building drum axis of revolution is within a specified precision distance of the work station working axis, i.e., alignment comprises making the tire building drum axis of revolution coincident with the work station working axis. Since the tire building drum is on a moving platform, it must maintain the desired alignment without imposing too great a weight burden on the moving platform. Furthermore, since the moving tire building drums may not be continuously connected to a power source, it is desirable that any drum support/stabilizer should be able to provide stabilizing support without the continuous application of power, be it electrical or air pressure or otherwise.
The present invention is intended to overcome the limitations of the prior art by providing method and apparatus for stabilizing a cantilever mounted tire building drum, particularly one that rotates, and particularly in the context of tire building drums that move from station to station through a flexible manufacturing system for tire building.